With most device applications, contacts need to be formed to both functional structures of the device as well as to the back end of line (BEOL) wiring. For instance, magnetic random access memory (MRAM) devices generally contain a plurality of magnetic memory cells. Contacts are needed to access these magnetic memory cells as well as the (BEOL) wiring adjacent to the magnetic memory cells.
Contact formation generally includes patterning trenches (e.g., in a dielectric) and then filing the trenches with a conductor to form the contacts. While fairly straightforward in theory, in practice this process can present some notable challenges. For instance, one wants to avoid either overetching or underetching the trenches. Namely, overetching beyond the contact region of a magnetic memory cell can undesirably result in a short between the device and the contact. Underetching results in the contact not reaching the magnetic memory cell, thus producing a non-functional device. The contact trenches are often formed using an etching process such as reactive ion etching (or RIE). Non-uniformity of the RIE across a wafer inevitably leads to over or underetching for some of the devices.
Given this variability in the etching process, it is thus extremely difficult to coordinate the processes needed to form contacts to the magnetic memory cells with those needed to form contacts to the BEOL wiring without resulting in some over or underetching of the cells. Accordingly, these two contact structures are typically formed separately from one another. Separate processes however undesirably add to production complexity and cost.
Thus, techniques effective for simultaneously forming contacts to both functional structures and BEOL wiring of a device would be desirable.